We have investigated the trans-epithelial transfer of milk immune cells to nursing pups and examined the result of transfer once the recipients were adult. Our novel approach used foster-nursing of non-transgenic mouse pups by green fluorescent protein (GFP) transgenic dams. The fate of GFP+ immune cells in the pups was followed at 1, 2, 3, and 4 weeks by FACS analysis, immunohistochemistry, and RT-PCR. Despite high numbers of GFP+ B cells and macrophages in milk, these cells were not observed undergoing trans-epithelial migration. Eighty percent of the GFP+ cells observed crossing the small intestine of the pup at weeks 1 and 2 could be positively identified as CD8+ or CD4+ T cells. These T cells homed to the spleen and thymus, with maximal accumulation at 3-4 weeks, and disappearance thereafter. Because T cells were transferred, we examined whether sensitizing dams with an antigen that elicits a T cell-mediated delayed-type-hypersensitivity (DTH) response, would result in sensitization of adult offspring. This was not apparent. Instead, nursing by a sensitized dam amplified a subsequent DTH response in adult female offspring (compared to females nursed by a non-sensitized dam) and yet suppressed a subsequent DTH response in males (compared to males nursed by a non-sensitized dam). In other words, there was a long-lived effect of cell transfer on the DTH response that was different depending on the sex of the recipient. From analysis at later time points, it seems unlikely that the transferred cells became long-lived components of the recipient's immune system, but rather that information was transferred from dam to pup. We therefore hypothesize that transferred maternal cells affect T cell development, selection and expansion during neonatal T cell production. The long term objectives of this project are to determine the importance of maternal milk cell transfer to immune responses in offspring, especially as such transfer might relate a) to T cell development in general, b) to sexual dimorphism both in susceptibility to immune disease and the efficacy of immunization, and c) to the possibility of safely enhancing immunity in young children. The specific aims are 1) to further characterize the transfer of immune information from dam to pup relevant to the adult DTH response. In the process to a) test a working model of the mechanism and b) expand the study to include tuberculin as a disease-related antigen of greater significance to world health, 2) to determine whether the modulation of DTH responsivity is the result of a change in the balance of T cell subsets, and 3) using the novel four core genotype mouse model, to determine whether the sex effect is caused by sex chromosome complement or by the testis-determining gene, Sry. A similar physiological nursing approach is proposed to achieve these specific aims, with mechanistic interrogation enhanced by the addition of Rag1-/-, IL-10 null, IL17 receptor A null, or four core genotype mice as foster recipients of the milk. Congenic CD45.1 and CD45.2 dam and pup pairs will also be used. A team of senior investigators with expertise in prolactin endocrinology and endocrine regulation of immune responses (PI), immunopathology (Muller), mucosal immunology and central tolerance (Lo), and the biological basis of sex differences (Arnold) has been assembled to accomplish these aims. All members of the team are highly productive and respected members of their disciplines.